Supplementary Materials
Resistive switching of a TaOx/TaON double layer via ionic control of
carrier tunneling
Heeyoung Jeon,1 Jingyu Park,1 Woochool Jang,2 Hyunjung Kim,1
Chunho Kang,2,3 Hyoseok Song,2 Hyungtak Seo,4,a) and Hyeongtag
Jeon1,2,b)
1Department
2Division
3FAB
of Nano-scale Semiconductor Engineering, Hanyang University, Seoul, 133-791, Korea
of Materials Science and Engineering, Hanyang University, Seoul, 133-791, Korea
Manufacturing Division, SK Hynix Inc., 2091, Gyeongchung-daero, Bubal-eub, Icheon-si,
Gyeonggi-do, 167-701, Korea
4Department
of Materials Science and Engineering and Energy Systems Research, Ajou University,
Suwon, 443-739, Korea
1. Current-Voltage (I-V) Characteristics of a Pt/TaON/TaOx/Pt stack
The interface state is a significant factor in the proposed valence model for one of the resistive
switching mechanisms. To confirm the roles of the upper interface and lower interface, TaON
was inserted into each interface position separately. Self-compliant resistive switching was
also observed in the Pt/TaON/TaOx/Pt stack (i.e., TaON insertion at the upper interface). In
contrast to the TaON insertion at the lower interface, the reliability was less than that without
TaON insertion. The Pt/TaON/TaOx/Pt device was subject to breakdown within 10 repeated
switching cycles. This is due to the lower barrier height between TaOx and the bottom Pt
electrode. That is, without TaON at the lower interface, higher energy electrons are injected
from the bottom Pt to the channel TaOx oxide due to the lower barrier height.
2. Rutherford Back Scattering and Auger electron spectroscopy
RBS measurements were carried out to confirm the chemical composition of the 50-nm-thick
TaOx films deposited on the Si substrate. Only Ar gas was used to sputter the Ta2O5 ceramic
target and the chemical composition of the deposited TaOx film was Ta2O3.6, as shown in Fig.
S2(a). AES depth profile measurements were performed for the Pt/TaOx/TaON/Pt device to
identify the stack structure. The atomic sensitivity factor (ASF) of Ta was calibrated by RBS
data. Nitrogen was observed at the interface between the TaOx layer and the Pt bottom
electrode, as shown in Fig. S2(b).
3. Angle-Resolved X-ray Photoelectron Spectroscopy
Angle-resolved X-ray photoelectron spectroscopy (ARXPS) was utilized to analyze the
binding energy shift of TaOx, TaOx/TaON, and TaON layers at various tilt angles.
Figure S3 shows X-ray photoelectron spectra of Ta 4f peaks in TaOx, TaOx/TaON, and TaON
layers. The binding energy (BE) of Ta4f in the TaOx layer was 26 eV, which indicates that the
oxidation state of Ta is +5. As the TaON was inserted, the binding energy was negatively shifted
at all tilt angles. This charge transfer also affects the valence band edge state. At all tilt angles
corresponding to both the surface and interface, a lower BE is noted in the presence of TaON
compared to TaOx alone, implying a nitrogen effect.
4. Poole-Frenkel emission model fitting
Figure S4(a) shows the fitting results for ln(I/V) versus V1/2 in HRS of the Pt/TaOx/Pt under a
positive bias at different temperature. Figure S4(b) shows ln(I/V) versus 1/kT for different
biases and the activation energy (Ea) was extracted from the slope of Figure 6b. After that, Ea
was plotted as a function of V1/2 as shown in Fig. S4(c). Extrapolating the curve of Fig. S4(c)
to the zero bias, the trap energy (Et) was extracted to be about 0.154 eV and the dielectric
constant for TaOx was extracted to be about 17.4 from the slope of Fig. S4(c). This extracted
dielectric constant is similar value with known value for TaOx. Therefore, P-F model is
reasonable for Pt/TaOx/Pt single layer geometry. However, the extracted value of Et is not
consistent with obtained by SE (Fig. 4(c)) and this implies that there can be additional defect
associated charge transport mechanism; that is most probably trap-assisted tunneling (TAT).
By combining I-V, chemical, and electronic structure analyses, the final transport mechanism
is suggested, as shown in Fig. S4(d), (e), and (f). Based on SE and XPS analyses, schematic
band alignment of TaOx and TaOx/TaON with top and bottom Pt electrodes are indicated in
Fig. S4(d), (e), and (f). In the Pt/TaOx/Pt, P-F emission concurrently occurred with TAT as
shown in Fig. S4(d). However, carrier transport mechanism change is led by TaON insertion,
which improves resistive switching characteristic by P-F mixed with TAT (TaOx single layer).
In the low bias regime, the electron transport mainly occurs by DT in TaON due to lack of
localized defects and P-F mixed with TAT to the TaOx level from the Pt 6s state, as proposed
in Fig. S4(e). However, in the high bias regime, the electron transport occurs by DT in TaON
and hot carrier phonon scattering at conduction band TaOx. This process affects the value of
Ea as a function of voltage (Fig. S4). After that, P-F mixed with TAT occurs in TaOx, as
proposed in Fig. S4(f).
In this supplementary information, the I-V characteristics of the Pt/TaON/TaOx/Pt stack,
physical properties of Pt/TaOx/Pt and Pt/TaOx/TaON/Pt stack, raw Ta 4f XPS spectra of TaOx,
TaON/TaOx, and TaON layers, and Poole-Frenkel emission model fitting results for
Pt/TaOx/Pt and Pt/TaOx/TaON/Pt are provided.
Fig. S1. I-V characteristics of Pt/TaON/TaOx/Pt stack. (a) Schematic diagram of
Pt/TaON/TaOx/Pt stack. (b) Conventional I-V characteristics.
Fig. S2. (a) RBS spectra of 50-nm-thick TaOx films deposited on the Si substrate. (b) A
ES depth profile of Pt/TaOx/TaON/Pt stack.
Fig. S3. Ta 4f XPS spectra and binding energy shift as a function of tilt angle of TaOx,
TaOx/TaON, and TaON layers. Ta 4f XPS spectra at various tilt angles for TaOx, TaOx/TaON,
and TaON. The 22.5° and 77.5° correspond to near interface (i.e., deep X-ray injection) and
surface, respectively.
Fig. S4. Poole-Frenkel emission model fitting results for Pt/TaOx/Pt: (a) ln(I/V) vs. sqrt(V) for
electron injection from bottom Pt under a positive bias. (b) ln(I/V) vs. 1/kT to extract the
activation energy (Ea). (c) Extrapolating Ea to zero bias, the trap energy is extracted from the
intersection on the y-axis. Schematic band diagram and carrier transport mechanisms for (d)
Pt/TaOx/Pt. (e) Pt/TaOx/TaON/Pt at low bias regime. (f) Pt/TaOx/TaON/Pt at high bias regime.
Fig. S5. Poole-Frenkel emission model fitting results for Pt/TaOx/TaON/Pt: (a) ln(I/V) vs.
sqrt(V) for electron injection from bottom Pt under a positive bias. (b) ln(I/V) vs. 1/kT to extract
the activation energy (Ea). (c) Extrapolating Ea to zero bias, the trap energy is extracted from
the intersection on the y-axis.